1. Field of the Invention
The present invention relates to an image forming apparatus of the type capable of forming images on both sides of a sheet or recording medium, and an image forming system including the same.
2. Description of the Background Art
An image forming apparatus of the type described is implemented as, e.g., an electronic copier, a printer, a facsimile apparatus or a multifunction machine having at least two of such functions. This type of apparatus is generally constructed to transfer a first image from an image carrier to one side of a sheet, fix the image on the sheet, reverse the sheet to thereby again deliver it to the image carrier, transfer a second image from the image carrier to the other side of the sheet, and then fix the second image to thereby produce a duplex print. However, the problem with this type of apparatus is that two times of delivery of a single sheet to the image carrier increases the overall image forming time and thereby lowers productivity.
In light of the above, Japanese Patent Laid-Open Publication No. 11-295937, for example, discloses an image forming apparatus including an intermediate image transfer belt and a first and a second image carrier. An image formed on the first image carrier is transferred to the intermediate image transfer belt while an image formed on the second image carrier is directly transferred to one side of a sheet. The image transferred to the intermediate image transfer belt is transferred to the other side of the same sheet. This successfully reduces image forming time in a duplex print mode for thereby enhancing productivity.
In the image forming apparatus disclosed in the above document, the intermediate image transfer belt is elongate in the up-and-down direction, preventing the apparatus from increasing in size in the horizontal direction. However, a sheet feeder loaded with a stack of sheets is positioned below the intermediate image transfer belt. This brings about a problem that when a plurality of sheet feeders are arranged one above the other, the overall height of the apparatus noticeably increases, making it difficult for the user to operate the apparatus. Moreover, such a height of the apparatus makes the apparatus unstable when installed at the user's station. This problem becomes more serious when a plurality of first image carriers and a plurality of second image carriers are arranged at both sides of the intermediate image transfer belt.
Technologies relating to the present invention are also disclosed in, e.g., Japanese Patent Laid-Open Publication Nos. 8-97962, 10-39550, 11-24330, 11-202565 and 11-295937.